Sonography has a high negative predictive value (NPV) and should be considered as a reasonable screening tool in the evaluation of acute appendicitis, according to a study of pediatric patients in the December issue of the Journal of Ultrasound in Medicine.
While multiple studies have evaluated the use of sonography and CT for the diagnosis of appendicitis, Preeyacha Pacharn, MD, from the department of radiology at Siriraj Hospital in Bangkok, Thailand, and colleagues sought to determine whether it can be used as a screening tool to exclude acute appendicitis.
Because “[i]maging plays an important role in the modern evaluation of abdominal pain, … [t]he ideal imaging test would be readily available, fast, inexpensive, reproducible, safe and accurate,” the authors wrote.
The investigators retrospectively reviewed right lower quadrant sonograms of 193 patients (158 female; age range, three to 20 years) with suspected acute appendicitis over a one-year period. They graded the sonographic findings on a five-point scale, ranging from a normal appendix identified (grade 1) to frankly acute appendicitis (grade 5). They also compared sonographic findings with subsequent CT, surgical and pathologic findings; and assessed the diagnostic accuracy of sonography, considering surgical findings and clinical follow-up as reference standards.
Pacharn and colleagues found that 25.4 percent of the patients had appendicitis on sonography; 74.6 percent had negative sonographic findings.
As a follow-up, they obtained CT scans in 26.4 percent of patients within four days after sonography, and included 39 patients with negative and 12 with positive sonographic findings. CT changed the sonographic diagnosis in 10 patients: from negative to positive in three cases and positive to negative in seven.
Also, 43 patients underwent surgery. The surgical findings were positive for appendicitis in 86 percent of the 43 patients who had surgery. Patients with negative sonographic findings who, according to the authors, did not have subsequent CT scans or surgery were considered to have negative findings for appendicitis.
Finally, seven patients with negative sonographic findings underwent surgery and had appendicitis; therefore, 137 of 144 patients with negative sonographic findings did not have appendicitis.
On the basis of these numbers, Pacharn and colleagues concluded that the NPV was 95.1 percent.
“The role of sonography in screening algorithms for the evaluation of suspected acute appendicitis is supported, particularly in young female patients for whom the gonadal radiation dose should be kept to a minimum,” they wrote. “However, further imaging could be performed if clinical signs and symptoms worsen or strongly suggest appendicitis.”